1. Field of the Invention
The present invention relates to a device for adjusting a position of a beam receiving portion of a photo sensor provided in a signal sensing system of a magneto-optical disc device or an optical disc device, for example, a laser beam being radiated onto the beam receiving portion.
2. Description of the Related Art
In an optical disc device, an optical head must be controlled in such a manner that a spot radiated from a laser beam is focused on a recording portion of an optical disc, and is positioned at the center of a track on the optical disc. For this control, a focusing error signal and a tracking error signal are sensed while sensing information recorded on the optical disc. While the focusing error signal is sensed by am astigmatism method, a spot size method has been developed recently to detect the focusing error signal as disclosed in Japanese Unexamined Patent Publication No. 61-206944. The tracking error signal is sensed by a push-pull method.
The focusing error signal and tracking error signal are obtained as follows. Namely, the laser beam reflected from a track of the optical disc is received by a photo sensor which is divided into a plurality of beam receiving areas, and output signals of the divided beam receiving areas are processed and calculated, and thereby the focusing error signal and the tracking error signal are obtained.
In an initial setting (or adjusting) process of the optical disc device, under a condition in which the beam spot radiated onto the optical disc is in-focus and is positioned at a proper position on the track, the position of the optical system must be adjusted in such a manner that the beam reflected by the optical disc, and having the proper size, is radiated onto a proper portion a center portion, usually) of the photo sensor. Since the focusing error signal and the tracking error signal are obtained by detecting changes in form, size and position of the beam spot radiated onto the photo sensor, and the changes are obtained by combining the signals outputted from each of the receiving areas of the photo sensor. Therefore, the initial positions of the sensing system including the photo sensor, a condensor lens and a beam splitter are required to be adjusted with a high degree of accuracy.
Conventionally, in the positional adjustment of the sensing system, the condenser lens is displaced along the optical axis thereof, and the photo sensor is moved in vertical and horizontal directions which are perpendicular to the optical axis. The adjustment in the conventional device is carried out for each sensing operation, i.e., reading of information recorded on the optical disk, sensing of the focusing error signal, and sensing of the tracking error signal. Therefore, the number of portions which should be adjusted are too numerous which makes the adjusting operation cumbersome, and adjusting mechanisms must be provided at too many positions which increases the number of parts of the sensing system.